The invention relates to a method of separating the constituents of the blood (full blood) which is taken adjustably from a donor "in vivo", adjustably mixed with anticoagulants supplied to a speed-adjustable blood centrifuge from which the separated constituents (blood fractions) are adjustably withdrawn and thereafter partly collected and partly returned to the donor, wherein the flow rates of the full blood and of the fractions are measured and automatically adjusted so that an optimum separation takes place.
The invention further relates to an apparatus for carrying out the method.
In separating systems of this type it is important for the flows of the full blood and the blood fractions to be in a correct ratio to each other and the fractions to include to a great extent only the separated constituent, i.e. the so-called separating boundary (the boundary between red blood corpuscles and the other fractions) in the blood centrifuge to be located at an optimum position.
A separating system of the aforementioned type is known from U.S. Pat. No. 3,489,145 and explained in all details therein.
The control arrangements provided in the known case for the apparatuses setting the flow rates (and including in particular delivery pumps) and the speed of rotation regulator of the centrifuge permit a separate setting of the flow rates of the associated delivered media and a speed of rotation setting of the centrifuge to take account of the aforementioned conditions.
Associated with the centrifuge is a buffer container for the full blood provided with anticoagulants, said container having a level control which automatically interrupts the supply of full blood when a predetermined amount of full blood is disposed in the buffer container.
In spite of this partial automation (level control) a disadvantage in the known case is that it is left to the operator to actuate the control or regulating means to ensure an optimum setting and retain this setting over longer periods of time (subsequent adjustment). The operator visually supervises the separating boundary. At a given speed of rotation of the centrifuge via a change of the delivery speed of the individual blood fractions with respect to each other, i.e. a change of the speeds of rotation of the associated pumps, the separating boundary can be displaced (column 11, line 64, to column 12, line 3, of the U.S. patent).
This latter context is utilized in the system according to further known U.S. Pat. No. 4,151,844. A photoelectric sensing is provided which optically detects the location of the separating boundary and converts it to an electrical signal which is compared with a desired value; the difference acts via a digital controller on a positioning member which oppositely alters the setting of the means for transporting the fractions in dependence upon the magnitude and amount and direction of the rise of the optical density at the separating boundary.
The aforementioned U.S. patent does not given any details on the control of the other apparatus and the centrifuge itself.
This known principle of automatic regulation of the separating boundary as controlled variable via a photoelectric ratio control of the flow rates of the withdrawn fractions has the considerable disadvantage that it does not include the other variable system parameters in the automatic control. Fluctuations in the full blood supply and the centrifuge speed of rotation can thus only be eliminated in unsatisfactory manner. Furthermore, the system setting possibilities (variation width of the setting possibilities in the system) are considerably limited.
DE-OS No. 2,845,399 discloses a further separating system, that set forth at the beginning from which the invention proceeds.
In this system the system known from the first mentioned U.S. Pat. No. 3,489,145 has been practically automated such that at a predetermined speed of rotation the flow rates of the full blood and of the fractions are set with respect to each other so that an optimum separation is effected in dependence upon the response of an optical sensor on mixing the fractions (hematocritic supervision analogous to the second U.S. patent mentioned). In the known separating system the centrifuge is set to a predetermined speed of rotation so that with a full blood flow set as desired specific fraction volumes occur whose unmixed withdrawal must be controlled and monitored by the automatic control system. The withdrawal speeds of the fractions necessary for unmixed separation must therefore be determined, i.e. it is necessary for a given speed and given full blood flow to determine the proportion of the individual fractions and set the withdrawal corresponding to said determination. On any change of the full blood flow the known system must therefore carry out a complete new determination of the fractions occurring.
Thus, in the known case long control times result and it is therefore not possible to set the full blood flow very rapidly in accordance with the donor or blood pressure or even change it during a separation. Moreover, in extremely unfavourable cases it may even happen that the speed of rotation of the centrifuge has been so unfavourably selected for the selected full blood flow that one of the desired fractions does not accumulate at all and thus cannot be withdrawn.